Higher Unit 3 Electrolysis. After today’s lesson you should be able to:  Use ‘Q = I x t’ to calculate - the value of faraday - the mass of product at.

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Presentation on theme: "Higher Unit 3 Electrolysis. After today’s lesson you should be able to:  Use ‘Q = I x t’ to calculate - the value of faraday - the mass of product at."— Presentation transcript:

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After today’s lesson you should be able to:  Use ‘Q = I x t’ to calculate - the value of faraday - the mass of product at an electrode - the time or current used in the experiment - the volume of gas given off at an electrode - the charge on an ion

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Electrolysis  Electrolysis is a chemical reaction which occurs when an ionic compound is broken down into its elements using electricity.  The ionic compound must be molten or in solution.  A d.c. supply is used to separate the products to different electrodes.  Positive ions are attracted to the negative electrode where they undergo reduction.  Negative ions are attracted to the positive electrode where they undergo oxidation.

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 The current, symbol ‘I’, is the speed at which the electrical current flows round the circuit.  Current is measured in Amperes (A).  The current is kept constant by using a variable resistor in the circuit.  The electrical charge, symbol ‘Q’ is measured in Coulombs (C).  The time the current has been flowing round the circuit, symbol ‘t’, is measured in seconds (s).  The total charge is calculated using the equation Q = It

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Electrons and Faradays  The charge is carried through the wires of the circuit (the external circuit) by electrons.  1 mole of electrons = 1 Faraday = 96500C.  The ion-electron equation for the element being calculated gives the number of moles of electrons and hence, the number of Faradays required to deposit 1 mole of the element.  e.g. Cu 2+ + 2e - → Cu. 1 mole of copper is deposited using 2 moles of electrons = 2 x 96500C = 193000C.

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Example 1 – Calculating the Faraday experimentally  A solution of copper(II) nitrate was electrolysed for 20 mins using a current of 0.2A. A mass of 0.08g of copper was deposited on the negative electrode. Calculate the value of the Faraday.

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Example 4 What volume of hydrogen would be given off at the negative electrode in the electrolysis of an aqueous solution if a current of 0.25A flowed for 2hrs. (molar volume of hydrogen = 24 l mol -1 )